The present invention relates generally to a four wheel drive for a motor vehicle and more particularly to an arrangement which is spatially more compact.
Reference is made to German Patent Application No. P 38 35 223.0 filed in Germany on Oct. 13, 1989, a corresponding U.S. application Ser. No. 07/421,327 being filed in the U.S. on even date therewith.
A four wheel drive arrangement is described in German Patent Specification (DE-PS) 32 12 495 in which a planet gear transfer transmission is driven by a gear shift transmission by way of an input shaft. An output shaft to a rear axle, which is driven continuously, is disposed coaxially to the input shaft. When a clutch is engaged, a disk brake is operated which acts upon the transfer transmission, and a second output shaft is connected which is disposed in parallel to the input shaft. A chain drive is used for the transmitting of motion to the second output shaft.
From European Patent Application (EP-A) 0 216 318, a four wheel drive is disclosed having a locking system including a planetary transmission and a bundle of disks which can be pressed against its planet carrier in a frictionally engaged manner. A first output shaft of the locking system, which is constructed as a hollow shaft, is disposed concentrically with respect to an input shaft. A second output shaft is disposed coaxially to it. The input shaft and the two output shafts are disposed in bearings of a stationary housing.
Accordingly, it is an object of the present invention to provide a four wheel drive of this type in a spatially more compact manner.
If the input shaft is constructed as a hollow shaft, and the first output shaft is disposed at it, and the second output shaft is disposed in the first output shaft, a four wheel drive, according to advantageous features of preferred embodiments of the present invention, can be housed in a very narrow space since bearings for the input shaft and the output shafts, which are fixed at the housing, are not absolutely necessary. By means of the appropriate dimensioning of the planet gear transfer transmission and of the disk brake, both components may have approximately the same outside diameter and with a narrow radial and axial play, may be surrounded by a cylindrical lock housing. The flux of force moves from the input shaft to the lock housing and to the planet carrier which is non-rotatable with respect to it. The planet gears disposed at the planet carrier, on one side, are engaged with the ring gear which is non-rotatable with respect to the first output shaft and, on the other side, are engaged with the sun gear which is non-rotatable on the second output shaft.
According to the selection of the gearings at the planetary transmission, a torque distribution takes place to the two output shafts of the four wheel locking system leading to the rear axle and to the front axle. A torque distribution of about 31/69 (front/rear) has proven to be particularly advantageous. After a given slip difference was reached, by means of the operating of the disk brake, the drive torque is redistributed from the axle with the higher slip to the other axle.
Other characteristics developing embodiments of the invention, which concern the bearing and the guiding of oil in the four wheel locking system, are also envisioned.